Terminals (User Equipments/Mobile Stations) are often equipped with capabilities for access via 2G/3G and WLAN. Other equipments, such as a laptop, may have capabilities for access via HSPA (High Speed Packet Access)/LTE (Long Term Evolution), WLAN (Wireless LAN) and Ethernet. Typically the terminal or laptop uses different accesses one at a time. And more importantly, a given service or a given IP session is only using one access at a time.
Currently 3GPP EPS (Evolved Packet System), also known as 3GPP SAE, is defining solutions for how session continuity can be achieved when a UE moves between different accesses. This can e.g. mean that a service that is running over a cellular access is moved to run over a WLAN access instead. But also with this solution, the UE is only using one access at a time and during an access change, the whole IP session and all running services within that IP session is moved from source access to target access.
Simultaneous use of multiple accesses (a.k.a. multihoming) is not supported, except for very short times during a handover between two accesses. Multihoming is a term used for techniques intended to increase the reliability of the internet connection for an IP network. Now the scenario where a terminal (UE/MS) can get simultaneous access over a variety of access networks is gaining more interest.
There is work ongoing in IETF (Internet Engineering Task Force) for defining mobility solutions in multihoming scenarios. Related work has also been started up in 3GPP. As part of this work the concept of “flow mobility” is investigated. This means that i.e. only a subset of the IP flows for a given IP session is moved from one access to another. For example, it could be that only the video component of a multimedia call is moved from cellular access to WLAN, while the IP flows related to the voice component of the same call stays in cellular access. Some services, e.g. telephony or audio/video streaming require resources to be reserved in the target access in order to provide acceptable quality of experience to the end user(s).
However, it is difficult to predict availability of resources in mobile networks where congestions and bandwidth variations can occur at any point in time. QoS (Quality of Service) mechanisms have been developed to address the needs that services sensitive to bandwidth variations and delay have. However, once QoS mechanisms come into play some subscriber's will be favored over others. This may result in a decreased level of perception for some subscribers, while others will not experience any changes.
The problem is therefore that the current network solutions (such as QoS) are very terminal centric and does not take full advantage of the existing network architecture.